(1) Field of the Invention
The present invention relates generally to an apparatus and a process for laser coating of the inner diameter of tubes.
(2) Description of the Related Art
Industrial coating or cladding of tubes is well known. In the oil and drilling industry, tubes of various sizes often demand inner diameter coating, welding or cladding with a desired material. Lasers have been utilized as a coating process by melting the coating material with the desired surface to generate a “melt pool” which subsequently hardens.
Laser welding of the inner diameter (ID) of barrels involves the depositing of a liner material prior to welding in the form of paste or powder, or a separate liner tube. In the alternative, during this welding process a powder or continuous wire is applied to the surface receiving the lining. The laser welder usually includes a laser beam delivered from a remote source via fiber optics and optical systems, or by direct laser beams.
Several systems to laser clad the inner surface of pipes have been developed and commercialized. These include U.S. Pat. Nos. 5,196,272; 5,387,292, 5,426,278, 5,496,422, 5,653,897, and 5,656,185. These systems are designed to repair damaged or corroded heat exchanger tubes in power generation plants. This is done by making short, localized repairs in relatively long, fixed pipes that cannot rotate. Each of these systems uses a rotating laser head for welding.
The systems described in the aforementioned patents include the insertion of a cladding or inlay material by any of a wire, powder, paste, or thin wall tube. The paste and the tubes must already be in place before the laser cladding operation. Powder is difficult to introduce in the vertical position without gravity assist since it tends to clog and interrupt the cladding process.
U.S. Patent Application No. 2007/0056939 to Colby et al.; U.S. Pat. No. 6,881,451 to Heinemann et al.; U.S. Pat. No. 6,858,262 to Fischer et al. and U.S. Pat. No. 6,548,125 to Warnecke, each describe inventions related to powder coating using lasers. U.S. Patent Application No. 2007/0056939 application describes laser cladding of tubes at very high revolution speeds, 100-10,000 rpm. Particularly, this application is related to liners on plasticating barrels. U.S. Pat. No. 6,881,451 describes laser coating the internal surface of a piston of an internal combustion engine by rotating the laser within the piston. U.S. Pat. No. 6,858,262 describes laser coating of a cylinder by displacing the laser and powder apparatus axially along the cylinder. U.S. Pat. No. 6,548,125 describes laser coating of a barrel of a weapon by moving the laser axially within the barrel.
For prolonged or full-length cladding of longer pipes, the head and especially the reflecting mirrors associated with a particular laser cladding apparatus must be cooled. This can be done using a cooling fluid such as air or water. Many of the previously described devices must have auxiliary services introduced from the laser head end of the tube because access from the opposite end is not available, and cannot be coordinated with the activity provided from the laser end. These auxiliary services can include a fiber optical viewer, wire/powder feeds, cooling media, optics (lenses) and focusing devices. Moreover, many of the known devices weld on constantly changing surfaces. This tends to give a non-uniform and less smooth surface due to the influence of gravity. If the cladding is done with the pipe in a vertical position, the melt pool tends to not be flattened and can have exaggerated rings or other distortions in the surface. There is no natural tendency to flatten or smooth the surface in a uniform manner.
U.S. Pat. No. 5,430,270 issued to Findlan et al. describes a method and apparatus for repairing damaged tubes using a laser welding technique. Particularly, this process describes clad welding and repair of the internal surface of a tube. The technique uses the addition of filler metal to build up the internal surface of the tube. A laser energy source is connected to an elongated weld head by an optical fiber. The weld head is rotatable and contains a mirror canted at a forty-five (45) degree angle. As the weld head rotates, the laser beam travels circumferentially around the inner surface of the tube. Metal fill material is fed to the location where the focused laser beam contacts the surface of the tube.
U.S. Pat. No. 5,179,260 issued to Kroehnert relates to a process and device for laser welding of a tube. Particularly, the device is constructed to prevent the laser from reflecting from the surface of contact back into the welding head causing thermal dysfunction and stress on the internal welding head components. Melted material from the welding process often reflects back onto the mirror of reflection and other components in close proximity. By using a reflected surface constructed to deflect the laser beam to a focal point at an oblique angle, the life and usage of the device is significantly increased.
Cladding head technology is known in the art. U.S. Patent Application 2007/0071907 to Stiles et al. describes a process for hard coating of ferrous metal substrates using a laser beam with diamond particles in a metal matrix produced from precursor powders of metals which bond to the diamond particles and to the ferrous substrate. The process utilizes a cladding head for delivering the laser beam. U.S. Pat. No. 6,316,744 to Nowotny et al. describes a machining head and a process for the surface machining of workpieces by means of a laser beam, in which coating, alloying in the area close to the surface or dispersion of a peripheral zone of the base material with powder particles can be carried out using a pulverulent filler supplied. Both references are incorporated by reference herein in their entirety.
Despite efforts to date, a need remains for an efficient and effective laser welding device and process for coating and/or cladding the inner surface of tubes. Particularly, a need exists for a programmable device that facilitates desired overlap of the cladding material. Still further, a need exists for easily replaceable parts and significant reduction of reflection of melted material back onto the optical components of a welding apparatus.
Objects
Therefore, it is an object of the present invention to provide an improved apparatus and process for laser coating/cladding of the inner surface of tubes.